---
name: "Parsing"
section: "3o"
platform: "linux"
package: "ocaml"
version: "5.5.0-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/Parsing"
---

# Parsing(3o)

The run-time library for parsers generated by ocamlyacc.

## NAME

Parsing - The run-time library for parsers generated by ocamlyacc.

## Module

Module   Parsing

## Documentation

Module **Parsing**\
  :  **sig end**

The run-time library for parsers generated by  **ocamlyacc** .

*val symbol\_start* :  **unit -\> int**

**symbol\_start** and  **Parsing.symbol\_end** are to be called in the action part of a grammar rule only. They return the offset of the string that matches the left-hand side of the rule:  **symbol\_start()** returns the offset of the first character;  **symbol\_end()** returns the offset after the last character. The first character in a file is at offset 0.

*val symbol\_end* :  **unit -\> int**

See  **Parsing.symbol\_start** .

*val rhs\_start* :  **int -\> int**

Same as  **Parsing.symbol\_start** and  **Parsing.symbol\_end** , but return the offset of the string matching the  **n** th item on the right-hand side of the rule, where  **n** is the integer parameter to  **rhs\_start** and  **rhs\_end** .  **n** is 1 for the leftmost item.

*val rhs\_end* :  **int -\> int**

See  **Parsing.rhs\_start** .

*val symbol\_start\_pos* :  **unit -\> Lexing.position**

Same as  **symbol\_start** , but return a  **position** instead of an offset.

*val symbol\_end\_pos* :  **unit -\> Lexing.position**

Same as  **symbol\_end** , but return a  **position** instead of an offset.

*val rhs\_start\_pos* :  **int -\> Lexing.position**

Same as  **rhs\_start** , but return a  **position** instead of an offset.

*val rhs\_end\_pos* :  **int -\> Lexing.position**

Same as  **rhs\_end** , but return a  **position** instead of an offset.

*val clear\_parser* :  **unit -\> unit**

Empty the parser stack. Call it just after a parsing function has returned, to remove all pointers from the parser stack to structures that were built by semantic actions during parsing. This is optional, but lowers the memory requirements of the programs.

*exception Parse\_error*

Raised when a parser encounters a syntax error. Can also be raised from the action part of a grammar rule, to initiate error recovery.

*val set\_trace* :  **bool -\> bool**

Control debugging support for  **ocamlyacc** -generated parsers. After  **Parsing.set\_trace true** , the pushdown automaton that executes the parsers prints a trace of its actions (reading a token, shifting a state, reducing by a rule) on standard output. **Parsing.set\_trace false** turns this debugging trace off. The boolean returned is the previous state of the trace flag.

**Since** 3.11